Narrowband two-color photon pairs are required in quantum repeater to overcome current limitations of long distance quantum communication. One photon is to address the visible or near infrared absorption line of the storage medium in a quantum memory (QM) and the other can be transmitted over a telecommunication fiber network. The practical prospect of quantum communication and information processing relies on sophisticated single photon pairs which feature controllable waveform, narrow spectrum, excellent purity, fiber compatibility and miniaturized design. One promising approach to generate such narrowband photon pairs is to use resonance enhancement of PDC within a resonant waveguide.
As partner within the European QuReP project ( www.quantumrepeaters.eu ) we are currently developing integrated PDC sources which match the absorption lines of Nd-based ( λ ≈ 880nm) and Tm-based ( λ ≈ 793nm) quantum memories.
A periodically poled lithium niobate (PPLN) waveguide with dielectric mirrors deposited on its end-faces has been demonstrated to integrated single-longitudinal-mode non-degenerate narrowband photon pair source. The source consists of a Ti-indiffused periodically poled lithium niobate (Ti:PPLN) waveguide and dielectric mirrors deposited on the waveguide end-faces, as shown in Fig.2. The first-order type II PDC phase-matching was chosen to generate TE-polarized signal photons around 880 nm and TM-polarized photons around 1345 nm when pumped at 532 nm in TE-polarization. It has been obtained when the poling period is around 4.4 µm.